Take help of your teachers to make a working model of Hope's apparatus and perform the experiment.Verify the result you obtain
Answers
Aim--The goal of this experiment is to demonstrate that between the temperatures 0 °C and 4 °C, the density of water increases with increasing temperature.
(To be exact: we are going to demonstrate that water has a higher density at 4 °C than at 0 °C.)
Procedure--
1. At least one hour before conducting the experiment, we fill one beaker with water and put it into a fridge. We do the same with an empty Hope's device. This way, we will precool the necessary parts of the experiment.
2. Right before the experiment itself, we prepare the cooling mixture using crushed ice and kitchen salt; the procedure is described in detail in the experiment ,cooling mixture of water ice and salt.It is appropriate to have a thermometer to control the temperature of the mixture.
3. After a thorough cooling we take Hope's device out of the fridge, isolate it from the pad (e.g. with a styrofoam plate) and insert the thermometers into both holes.
4. We pour the precooled water into the inner cylinder. The thermometers should now show the same temperature. If a measurement in time is available, we start it now.
5. Now we fill the reservoir with the cooling mixture. After that we simply observe the development of temperatures measured by both thermometers.
Answer:
We all know that the density of solids is greater than liquids so it is expected that when a liquid becomes solid its density increases and it contracts. But water on cooling shows contraction till 4°C and after that expands and converts into ice which has a lower density than water (clear from the fact that ice floats on water). This anomalous (different) behavior of water can be demonstrated by the use of an instrument called Hope’s apparatus. In this experiment the temperature of the water-filled in a cylinder vessel is varied. It is conducted in two sets:
1. In the first set, the water is maintained at a temperature higher than 4°C, and the cylindrical vessel is filled with this water. The reading of the two thermometers is noted (it is observed to be the same in the beginning). Then freezing mixture containing ice and salt id added to the trough and after some time (say 30 minutes) temperature is noted. In this case, the temperature of the water in the lower part of the vessel below the trough is found to be less as compared to the upper part. It can be explained by keeping in mind that the addition of freezing mixture decreased the temperature of the water and due to an increase in density (above 4°C) the water at lower temperature sinks down resulting in a lowering of the temperature of the thermometer 2 as compared to the temperature of thermometer 1.
2. In the second set, the water is maintained to a temperature near to 4°C and filled in the cylinder. After the addition of the freezing mixture, the temperature of water drops below
4°C and it begins to expand thus comes to the upper part (remember, ice floats on water). Thus, the temperature of the upper part of the vessel decreases resulting in a lowering of the temperature of the thermometer 1 as compared to the temperature of the thermometer 2
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